1. Field of the Invention
The present invention relates generally to cardiac stimulation, and more particularly to an implantable electrode for stimulating and/or sensing electrical activity of the heart and employing an active fixation mechanism to secure the electrode in position relative to the cardiac tissue with which the electrode is intended to interact.
2. Prior Art
Patent publication DE No. 27 32 547 A1 of the Federal Republic of Germany illustrates the current state of the technology pertaining to active fixation of electrodes designed for implantation in a chamber of the heart for stimulating the cardiac muscle. According to the invention described in that publication, a fixing hook is associated with the electrode head of a catheter led and is arranged to be movable relative to the head. During the insertion phase the fixing hook, which possesses an intrinsic spring action, is restrained in a retracted position within the outer contour of the electrode head such that the overall lead assembly is readily advanced through the vein. The fixing hook may be held under this restraint by various means, for example by means of a blocking wire, and upon release, the tip of the hook is thrust to a position outside the contour of the electrode head. If necessary, the thrusting of the fixing hook tip into this position may be accomplished with the aid of further triggering means. In any event, the fixing hook is released by the implanting physician when the electrode is determined to be properly positioned within the selected chamber of the heart. In the released state, the fixing hook may be engaged in the cardiac tissue by twisting the electrode lead.
The practical implementation of such a lead with endocardial electrode and associated fixing hook is not achieved without difficulty, owing to the necessarily small dimensions of the electrode head and the lead. Considerable care is required in the manufacturing process to provide an active fixation mechanism in which the fixing hook is held within the outer contour of the electrode head for subsequent precise release.
It is a principal object of the present invention to provide an active fixation mechanism for an implantable electrode which avoids such disadvantages.
A more specific object of the present invention is to provide an active fixation electrode which can be readily manufactured in a simple manner, while retaining the desirable aspects of ease of insertion and engagement with cardiac tissue so as to be secure against dislodgement and to ensure good electrical stimulation.